1. Field
Exemplary embodiments relate to a phase changeable memory unit, a method of manufacturing a phase changeable memory unit and a method of manufacturing a phase changeable memory device. More particularly, exemplary embodiments relate to a phase changeable memory unit having an enhanced structure, a method of manufacturing a phase changeable memory unit having an enhanced structure and a method of manufacturing a phase changeable memory device having an enhanced structure.
2. Description of the Related Art
Generally, a phase changeable memory device (PRAM) stores data by using a difference in resistance between two states, namely, an amorphous state and a crystalline structure state, of a chalcogenide material which forms a phase changeable material. Namely, the phase changeable memory device stores data “0” or “1” with a reversible phase transition of a phase changeable material including a chalcogenide material. The crystalline structure and the amorphous state of a chalcogenide material have dramatically different electric resistivity, which is a basis of storing data. The reversible phase transition is generated by a magnitude and/or wave length of pulse applied to the phase changeable material. For example, the amorphous state has a high resistance used to represent a binary “0” and the crystalline structure has a low resistance state used to represent a binary “1.” A reset current transforming the phase changeable material into the amorphous state and a set current transforming the phase changeable material into the crystalline structure are delivered to the phase changeable material through a transistor or a diode on a substrate.
A confined structure in which a fine via hole exposing a lower electrode is filled with a phase changeable material to reduce a contact area of the phase changeable material and the lower electrode has been developed in order to reduce the set current and the reset current. A diameter of the via hole has been decreased, for example, to under about 50 nm, in order to enhance integration degree of the PRAM. However, when the via hole has a small diameter, it is not easy to fill the via hole.